Abstract: An air by-pass device for internal combustion engines comprising a first valve assembly positioned between the carburetor and the intake manifold and having a passageway providing fluid communication between the carburetor and manifold, and a valve member in the passageway for closing off the passageway to the fuel mixture, means for conveying ambient air to the intake manifold through the first valve assembly, a second valve assembly operatively connected with the air conveying means for controlling the flow of air therein, first and second solenoids for operating respectively the first and second valve assemblies simultaneously, and an electric line connecting the solenoids with a source of electric current and including switches responsive to the accelerator pedal position and the flow of air from the engine cooling fan so that when the accelerator pedal is released at a time when the air flow from the engine cooling fan exceeds the normal flow at idle, the solenoids will be energized for cutting off the f